A keyword is a term or phrase that captures the essence of the topic of a document. The automatic extraction of topically relevant keywords from textual documents, such as web pages, word processing files, emails, web-page snippets, and so on, is useful for a variety of applications.
For example, extracted keywords can be employed to catalog or index documents, and then used in a search to efficiently scan the cataloged or indexed items for documents topically relevant to a keyword. Another example is an advertiser who is looking for keywords in a set of documents, such as web pages, for use in contextual targeted advertising. In contextual targeted advertising, an advertiser seeks to insert advertisements into a web page being viewed by a potential customer, which are related to the context of the web page. This increases the chance the potential customer will be interested in the advertisement and so increase the overall effectiveness of the advertising effort. Yet another example is in the field of related searches. In a web-search, a user inputs a search query and a search engine returns search results. Along with the search results, the search engine sometimes also offers a small number of search suggestions to the user based on the query. Keywords extracted from web pages related to the query can be used as the basis for these search suggestions.